REPORT ON THE COPEPODA. 41 



Dana separated this form from its relatives, and gave it generic rank, simply on the 

 strength of its strongly produced rostrum, a character certainly insufficient of itself to 

 maintain the generic distinction. But as the fifth pair of feet (at any rate in Rhin- 

 calanus gigcis) presents some differences of structure, I have retained, provisionally, Prof. 

 Dana's name, though with much doubt as to the propriety of doing so. 



1. Rhincalanus cornutus, Dana (PI. VII. figs. 1-10). 



Rhincalanus cornutus, Dana, Crust. U.S. Expl. Exped., p. 1083, pi. lxxvii. fig. 2, a.d. 



Female. — Length, l-7th of an inch (3'5 mm.). Forehead very much produced, 

 attenuated, terminated by a triangular, slenderly furcate rostrum, between which and the 

 anterior part of the head, as seen laterally, is a deep sinus ; cephalothorax four or five 

 times as long as the abdomen, and very slender ; the posterior margins of all except the 

 first and last segments produced at each side into a sharp, backward-pointing spine. 

 Anterior antennae about one-fourth longer than the body, twenty-three-jointed, the basal 

 joint very long, one very long marginal seta near the base, one on the twelfth, four- 

 teenth, sixteenth, nineteenth, and twenty-first joints, two on the twenty-second, and a lash 

 of four or five at the apex of the last joint. Posterior foot-jaws (fig. 7) of no great length, 

 and in structure like those of Calanus; peduncle two-, flagellum five-jointed. Inner 

 branches of the first pair of swimming feet two-jointed (fig. 8), second joint of the 

 peduncle swollen at the inner side, and bearing a setose tuft ; outer branch bearing three 

 ciliated spines. The second, third, and fourth swimming feet have their inner branches 

 three-jointed, the outer branches destitute of marginal spines (fig. 9), except the first 

 joint, the outer margin of which is swollen and produced into an apical tooth ; the 

 terminal spines of the swimming feet are long, very slender, and have an extremely delicate 

 hyaline lamina extended along the outer margin, but are in no other respect distinguish- 

 able from the neighbouring setae. Fifth pair of feet (fig. 10) simple, three-jointed, short, 

 the last joint bearing two apical spines of unequal length, the larger of which is 

 marginally ciliated. Abdomen four-jointed (three-jointed, Dana), first segment about as 

 lnii a- as the following three, and spined at its postero-dorsal angle. Caudal lamina) about 

 twice as long as broad, setae aboul as long as the abdomen, except the second on the 

 left side, which is twice as long as the rest. 



That the specimens above described are females, I conclude, from the fact of sperma- 

 tophores having been seen attached to the abdomen of some of them. Amongst all the 

 specimens I have not been able to find any difference which appeared to me to be sexual, 

 except that in one or two no fifth pair of feet was discernible. I think, however, that 

 these examples were probably immature. It will be noticed that the number of segment 



(ZOOL. CHALL. EXP.— PART XXIII.— 1 883.) 2 G 



s 



